Agitator



J. C. THOMAS Oct. 26, 1965 AGITATOR 2 Sheets-Sheet 1 Filed Dec. 18, 1965 INVENTOR. J6 2/04/45 w ArrMA/[Vf Oct. 26, 1965 J. c. THOMAS 3,214,148

AGITATOR Filed Dec. 18, 1965 2 Sheets-Sheet 2 INVENTOR.

Unite 3,214,148 AGETATOR J. C. Thomas, 974 Topeka, Pasadena, Calif. Filed Dec. 18, 1963, Ser. No. 331,560 13 Claims. Cl. 259-441) This invention relates to fluid agitating and mixing ap paratus and, more particularly, to an agitator for mixing Stratified layers of gasoline and oil in the fuel tank for an outboard marine motor or the like,

For the purposes of illustration, this invention is de scribed herein in terms of a specific problem, namely mixing stratified gasoline and oil in a fuel tank for a marine engine. It is apparent, however, that the invention may be used to advantage whenever liquids are to be mixed inside a container.

Many internal combustion engines, and particularly those marine engines referred to as outboard engines, operate on a mixture of gasoline and lubricating oil. The oil in the fuel mixture is relied upon to provide lubrication for the moving parts of the engine in the absence of a separate lubricating system for the engine. Conventionally, the fuel and gasoline are mixed together prior to filling of the fuel tank. If the engine is operated soon after the tank is filled, there is no problem since the oil and the gasoline are adequately intermixed one with another. If, however, the fuel/ oil mixture is allowed to stand in the tank, it separates into two layers or strata of liquid in the tank so that if the engine is operated without recombining the fuel and oil, the proper mixture will not be supplied to the engine.

Prior to the development of this invention, there was no convenient method for intermixing oil and gasoline which had stratified in a fuel tank; the usual method of mixing the separated liquids involved emptying the fuel tank into a separate container in which the liquids were mixed. With the advent of high horsepower outboard marine engines, however, the fuel tanks have increased in size to such an extent that they cannot be conveniently handled. If gasoline and oil stratify within the tank, it is a difficult procedure to empty the tank for remixing the liquids.

This invention provides a structurally simple, economic and highly effective apparatus for mixing stratified layers of gasoline and motor oil inside the fuel tank for an outboard marine engine. The apparatus is independent of the structure of the fuel tank and therefore may be supplied as an accessory for use with existing fuel tanks. The device preferably is fabricated from materials which are resistant to corrosion, swelling, and other adverse phenomena by the action of water and hydrocarbons. The device includes a collapsible fuel mixing and agitating head which is insertable into the tank through the generally small diameter filling port of the tank. The invention also has the feature that the collapsible agitating head is retractible into the body of the device so that it is not damaged when the device is not bein used.

Generally speaking, this invention provides an agitator for mixing liquids and comprises a body member. The body member has a bore therethrough and a lower end adapted for engagement in the filling opening of a vessel containing the liquids to be mixed. The bore opens to the lower end of the body member. An operating shaft is engaged in the bore for reciprocal movement relative to the body member. The device also includes a collapsible agitator head secured to one end of the operating shaft. The agitator head is adapted for expansion by cooperation with the liquids to be mixed into an open condition wherein the head has a dimension transversely of the operating shaft greater than the filling opening of the vessel. The head is moved into its open condition when the operating shaft is reciprocated so that the head moves away from the body member. The agitator head is further adapted for collapsing into a closed condition when the operating shaft is moved in the opposite direction so that the agitator head is retractible into the body member bore so that the agitator is disengageable from the vessel.

The above-mentioned and other features of the invention are more fully set forth in the following detailed description of the invention taken in conjunction with the accompanying drawings wherein:

FIG. 1 is a cross-sectional elevation view of a mixing device according to this invention showing the agitator head in its retracted position;

FIG. 2 is a fragmentary cross-sectional elevation view showing the body member of the mixing device engaged in the opening of a fuel tank, for example, and showing the agitator head in its opened condition;

FIG. 3 is a cross-sectional elevation view of the lower end of the operating shaft according to a preferred embodiment of the invention;

FIG. 4 is an enlarged cross-section view taken along line IV-IV of FIG. 3;

FIG. 5 is a fragmentary cross-sectional illustration of the interconnection of the operating shaft and agitator head according to a second preferred embodiment of this invention; and

FIG. 6 is an enlarged cross-sectional elevation view of the apparatus shown in FIG. 1 illustrating means for biasing the operating shaft upwardly of the body member.

Referring to PEG. 1, a mixing device or agitator 10 is illustrated. The agitator includes an elongated tubular body member or housing 11 which preferably has an outer surface configured as a solid of revolution about an axis longitudinally of the body member. An axial bore 12 is formed through the agitator body member and includes an enlarged diameter portion 13 which opens to a lower end 14 of the device and extends partially along the bore. Preferably the junction between the bore and the bore enlarged diameter portion is a conically tapered shoulder 15. Adjacent the lower end thereof, the body member defines an enlarged boss or bulb portion 16 adapted to be grasped by one hand of an operator of the device. The lower end of the device defines an upwardly and outwardly flaring conical seating surface 17 adapted to be engaged with the edge of a filling port or opening 18 in an upper wall 19 of an outboard motor fuel tank. Surface 1'7 engages the entire periphery of fiiling port 18 so that fuel and oil are not splashed out of the tank as agitator 10 is operated. An upwardly and inwardly tapering conical surface 20 is defined by the lower end of the body member concentric to bore enlarged portion 13 for guiding a mixing and agitating head 35 into retracted position in the bore enlarged diameter portion, as shown in FIG. 1.

A circularly cylindrical elongated operating shaft is disposed in bore 12 of the body member for reciprocation relative to the body member. The shaft has an upper end 26 which is disposed above an upper end 27 of the body member and which carries an operating handle 28 adapted to be grasped in the other hand of an operator of the device so that the shaft may be reciprocated in the bore. An annular gasket 29 is disposed across the upper end of the body member and is held thereto by an annular internally threaded cap 30 which engages cooperating threads on the exterior surface of the upper end of the body member. Gasket 29 is provided to prevent fuel and oil from being ejected upwardly through the clearance between bore 12 and shaft 25.

An enlarged diameter bulb or boss element 31, having an outer diameter less than the diameter of the bore enlarged diameter portion 13 but greater than the diameter of bore 12; itself, is connected to the lower end of the operating shaft. Preferably, the junction between bulb 31 and shaft is defined by an upwardly and inwardly tapering conical surface 32 having the same pitch as shoulder 15. Shoulder 15 and surface 32 cooperate to prevent fuel entrained in the bore enlarged diameter portion above boss 31 from being pumped upwardly through bore 12 and cause such fuel to be forced downwardly out the lower end of the bore at surface 20. Vertical grooves 33 are formed in surface 32 to further assure that fuel is not pumped into bore 12. Boss 31 provides means for restricting the upward movement of the shaft relative to the body member and also constitutes a portion of means for securing mixing head to the operating shaft. A protuberance 34 is formed integral with the body member interiorly of the bore enlarged diameter portion just below shoulder 15 to cooperate with the lower extent of shaft bulb 31 to hold the operating shaft at its uppermost limit of reciprocation relative to the body member in a position corresponding to the retracted position of the agitator head, as shown in FIG. 1.

A flexible mixing or agitator head 35 is connected to the lower end of operating shaft 25. The mixing head is comprised of a plurality of substantially stiff elongated ribs 36 and a flexible membrane 37 which preferably integrally interconnects the ribs along substantially their entire lengths and maintains them in spaced apart relation at regularly spaced apart intervals about the extent of the head when the head is in its open condition as illustrated in FIGS. 2 and 3. The ribs and the membrane cooperate to impart a substantially cone-shaped configuration to the head when it is in the open condition. More specifically, it is preferred that six ribs 36 be provided so that, in its open condition, the mixing head has a hexagonal and slightly truncated pyramidal configuration. A plurality of apertures 38 are formed through the membrane between the ribs to provide increased fuel and oil mixing operation of the head. If desired, apertures 38 may be deleted from the head without departing from the scope of this invention.

The upper ends of the ribs cooperate with the structure of operating shaft boss 31 to define means for pivotally connecting the upper adjacent ends of the ribs to the operating shaft so that the ribs are movable from a first position (shown in FIG. 1) in which the ribs are aligned substantially axially of shaft 25 and lie within an imaginary cylindrical extension of boss 31, to a second position (illustrated in FIG. 3) in which the ribs extend downwardly radially from the lower end of the operating shaft. The ribs are movable into their second position by cooperation with the liquids interiorly of the fuel tank when the mixing head is disposed interiorly of the fuel tank and the operating shaft is moved downwardly relative to the agitator body member. To this end, the upper end of each rib extends a short distance beyond upper edge 39 of the membrane and terminates in a spherical boss 41 of diameter substantially greater than the diameter of the rib itself and which defines protuberances which extend in opposite directions laterally of the rib. A recess 42 is formed in the lower end of the shaft within the operating shaft boss 31. Preferably recess 42 is of circular configuration and is disposed transversely of and concentric to the axis of the shaft, as illustrated in FIG. 3. The lower extent of the recess is spaced above the lowermost extremity of boss 31 and the recess is closed by a wall 42 defining the under surface of shaft boss 31. A circular opening 43 is provided through wall 42 into the recess concentric to the axis of the shaft, as shown in FIG. 4. A plurality of slots are formed through wall 44 radially of opening 43 and extend from the opening to the extreme outer diameter of operating shaft boss 31 although the slots do not extend through the boss along the entire vertical extent of the recess (see FIG. 3). As is apparent from the following description, the lower end of operating shaft 31 defines a cage for receiving the rib bosses. FIG. 3 shows that the outer ends of slots 45 are configured to define stop means which, in cooperation with the rib configuration, limit the pivotal movement of the ribs away from alignment with the shaft.

The number of slots 45 is equal to the number of ribs in the mixing head. In order that mixing head 35 may be attached to shaft 25, opening 43 has a diameter at least as great as the diameter of the spherical bosses 41 at the upper end of the ribs. The mixing head is attached to the lower end of the operating shaft by passing each of the rib bosses through opening 43 and into cooperation with a respective one of slots 45, as shown in FIGS. 3 and 4. Once all the ribs are engaged with the lower end of the shaft, a plug 46 is inserted into the recess through opening 43 to close the opening. Preferably the plug is threaded into the lower end of the operating shaft coaxially thereof. As illustrated in FIG. 3, plug 46 extends axially of the shaft beyond the lower end thereof to a terminal end 47 which is spaced below recess wall 44 a distance greater than the height of the agitator head when the head is in its open condition, as shown in FIG. 3. Plug 46 therefore comprises rigid stop means for preventing engagement of the opened agitator head with a lower wall 48 of a fuel tank within which the agitator head is used. Stop plug 46 prevents damage to the flexible agitator head as might result if the lower ends of agitator head ribs 36 are brought forcefully into contact with the bottom of the fuel tank.

FIG. 5 illustrates a second preferred agitator rib configuration and a second preferred mechanism for pivotally connecting the ribs to the lower end of the operating shaft. The upper end of each rib 54B is offset laterally from the elongate extent of the rib to define a lug 51. The lugs are disposed in a recess 52 in the lower extent of an operating shaft boss 53 having a configuration similar to shaft boss 31 shown in FIGS. 1, 2, and 3. The recess is disposed concentric to the axis of the operating shaft and opens downwardly from boss 53 peripherally of a stop element 54 which is formed integral with operating shaft 55. The recess has a lower wall 56 disposed normal to the axis of the shaft and formed by a shoulder at the upper end of the stop element. Rib lugs 51 are engageable with surface 56 which defines means for limiting the pivotal movement of the ribs away from alignment with the shaft. A pin 57 is passed through the lug of each rib at approximately the junction of the lug with the elongate extent of the rib to pivotally mount the rib to boss 53. The pins are mounted in projections 58 extending inwardly of the recess from the boss.

Referring to FIGS. 1, 2, and 3, mixing or agitator head 35 normally is retracted into enlarged diameter portions 13 of the body member bore when agitator 10 is not in use. The mixing head is maintained in the retracted position by engagement of protuberance 34 with operating shaft boss 31. When it is desired to mix gasoline and oil which may have stratified interiorly of a fuel tank of an outboard engine, for example, the conical seating surface of the body member is engaged with the periphery of the fuel tank filling port. The operating shaft 25 is then moved downwardly so that the mixing head is moved out of the bore into the interior of the fuel tank. As the mixing head contacts the liquid inside the tank, the liquid tends to resist downward movement of the mixing head and opens the head into the mixing position thereof shown in FIG. 2 in which the mixing head has a dimension transversely of the shaft greater than the diameter of fuel tank filling port 13. Once the mixing head is disposed in the fuel tank, shaft 25 is reciprocated so that the head intermixes the stratified fluid inside the fuel tank on downward movements thereof and collapses into substantially the position shown in FIG. 1 on upward movements. Engagement of stop element 46 with the bottom of the fuel tank prevents damage to the mixing head and limits the downward movement of the head inside the tank. The agitator is easily removable from the fuel tank vantage.

since the mixing head is collapsible to a size allowing the head to be retracted into the body member.

Especially where liquids to be mixed are viscous, the resistance of the liquids to downward movement of the opened mixing head can be such that the flexible membrane of the head may tear, or the head may be so loaded as to be inverted similar to an umbrella on a windy day. In order to prevent inversion of the mixing head, a cord 60 of an inelastic filament is laced between the ribs at the lower ends thereof. As illustrated in FIG. 3, cord 60 is passed through apertured lugs 61 preferably formed integral with the inner extents of the ribs adjacent the lower ends thereof.

In order to simplify the operation of agitator 1t resilient means for biasing the operating shaft upwardly relative to the body member are interconnected between the shaft and the body member. Such means provide that force need be applied only downwardly of the operating shaft to effect mixing operation of the mixing head within a fuel tank. FIG. 6 shows a compression spring 65 disposed in a bore 66 extending coaxially of the operating shaft from the upper end thereof partially along the shaft. The spring is abutted against handle 28 at its upper end and against a stop pin 67 at its lower end. Pin 67 is passed through the body member and into bore 66 through a slot 68 formed lengthwise of the operating shaft.

It is preferred, especially where agitator It is to be used for mixing Stratified gasoline and oil in the fuel tank of an outboard motor for example, that the agitator be fabricated from materials which are resistant to rust, corrosion, swelling and the like by interaction with water and hydrocarbons. Accordingly, it is preferred that the body member, the operating shaft, the mixing head, and

the stop element all be fabricated from synthetic materials 5 or plastics such as nlyons, phenolic resins, or polyethylene, although other synthetic materials may be used to ad- Such materials also have the advantage that they cannot generate sparks when the device is operated or when the agitator is struck against metal.

While the invention has been described above in conjunction with specific apparatus and in conjunction with application of such apparatus, this has been by way of example only and is not to be considered as limiting the scope of this invention.

What is claimed is:

1. Apparatus for mixing stratified liquids internally of a tank containing the liquids comprising (a) a tubular body member having (1) a lower end configured for seating in a filling port into the tank, and

(2) an axial bore through the body member including an enlarged diameter portion opening to and extending from the lower end of the body member partially along the bore,

(b) a flexible substantially cone-shaped mixing head including 1) a plurality of substantially stiff ribs, and (2) a flexible membrane interconnecting the ribs along substantially their entire lengths, (c) an operating shaft disposed in the body member and movable reciprocally therein and having (1) an upper end disposed exteriorly of the bore, and

(2) means at the lower end thereof for pivotally connecting the adjacent ends of the mixing head ribs to the shaft so that each rib is movable from a first position aligned with the shaft within an imaginary cylinder of diameter no larger than the diameter of the bore enlarged diameter portion to a second position corresponding to a mixing condition of the mixing head wherein the ribs are inclined radially downwardly away from the shaft,

(d) a rigid stop member extended below the lower end of the shaft for a distance greater than the altitude of the cone, and

(e) an operating handle secured to the upper end of the shaft.

2. Apparatus for mixing stratified liquids internally of a tank containing the liquids comprising (a) a tubular body member having (1) a lower end configured for seating in a filling port into the tank, and

(2) an axial bore through the body member including an enlarged diameter portion opening to and extending from the lower end of the body member partially along the bore,

(b) a flexible substantially cone-shaped mixing head including (1) a plurality of substantially stiff ribs, and (2) a flexible membrane interconnecting the ribs along substantially their entire lengths,

(c) an operating shaft disposed in the body member and movable reciprocally therein and having (1) an upper end disposed exteriorly of the bore,

and (2) means at the lower end thereof for pivotally connecting the adjacent ends of the mixing head ribs to the shaft so that each rib is movable from (i) a first position aligned with the shaft within an imaginary cylinder of diameter no greater than the diameter of the bore enlarged diameter portion whereby the shaft and head is retractible into the bore enlarged diameter portion, to (ii) a second position corresponding to a mixing condition of the mixing head wherein the ribs are inclined radially downwardly away from the shaft,

((1) a rigid stop member extended from the lower end of the shaft for a distance greater than the altitude of the cone,

(e) means carried by the body member for maintaining the shaft in a position relative thereto corresponding to the retracted condition of the mixing head in the bore, and

(f) an operating handle secured to the upper end of the shaft.

3. Apparatus according to claim 2 wherein the upper ends of the ribs adjacent the apex of the cone define enlarged protuberances extending laterally of the ribs, and the means at the lower end of the operating shaft defines a cage within which the upper ends of the ribs are disposed and from which the ribs extend, the protuberances pivotally retaining the rib upper ends in the cage.

4. Apparatus according to claim 3 wherein the cage defines stop means for limiting movement of the ribs away from alignment with the shaft.

5. Apparatus according to claim 2 wherein the means at the lower end of the shaft includes a recess circumferentially of the shaft, the upper ends of the ribs being disposed in the recess, and means for pivotally pinning the upper ends of the ribs to the shaft in the recess.

6. Apparatus according to claim 5 wherein each rib extends beyond the pinning means to define a lug, and the recess is configured to define a shoulder on the shaft disposed relative to the pinning means so that the lugs are engageable with the shoulder to limit the pivotal move ment of the ribs away from alignment with the shaft.

7. Apparatus for mixing stratified gasoline and oil inter- ,nally of a fuel tank of a motorboat and the like comprising (a) a tubular body member having (1) a lower end configured for seating in a filling port into the tank, and

(2) an axial bore through the body member including an enlarged diameter portion opening to and extending from the lower end of the body member partially along the bore,

(b) a flexible substantially cone-shaped mixing head including (1) a plurality of substantially stiff ribs, and

(2) a flexible membrane interconnecting the ribs along substantially their entire lengths,

(c) an operating shaft disposed in the body member and movable reciprocally therein and having (1) an upper end disposed exteriorly of the bore,

and

(2) means at the lower end thereof for pivotally connecting the adjacent ends of the mixing head ribs to the shaft so that the ribs are movable from a first head-closed position in which the head is retracti'ble into the body member to a second head-open and mixing position in which the ribs extend downwardly radially from the shaft,

(d) a substantially inelastic cord interconnecting the lower ends of the ribs for preventing inversion of the head by force acting upwardly on the .head when the head is in its open mixing condition, and

(e) an operating handle secured to the upper end of the shaft.

8. Apparatus for mixing stratified gasoline and oil internally of a fuel tank of a motor boat and the like comprising (a) a tubular body member fabricated of material resistant to rust and to corrosion by hydrocarbon fluids having (1) a bore axially therethrough,

(2) a lower end defining an upwardly and outwardly extending first conical surface substantially concentric to the lower end of the bore adapted for engagement peripherally of the edge of a filling port into the tank, and

(3) an upwardly and inwardly extending second conical surface disposed concentrically of and extending to the bore at the body member lower end,

(4) the bore having an enlarged diameter portion opening to the second conical surface and extending therefrom partially along the bore,

(b) a flexible substantially cone-shaped mixing head including (1) a plurality of ribs converging toward the apex of the cone, and fabricated of material resistant to rust and to corrosion by hydrocarbon fluids, and

(2) a flexible membrane interconnecting the ribs along substantially their entire lengths and maintaining the ribs in spaced apart relation about the extent of the mixing head,

(c) an operating shaft fabricated of material resistant to rust and to corrosion by hydrocarbon fluids disposed in the body member and movable reciprocally therein and having (1) an upper end disposed exteriorly of the bore,

and

(2) means at the lower end thereof for pivotally connecting the adjacent ends of the mixing head ribs to the shaft so that each rib is movable from a first position aligned with the shaft to a second position inclined downwardly away from the shaft, the second position of the ribs corresponding to a mixing condition of the mixing head,

(i) said means being slightly smaller in diameter than the enlarged diameter portion of the bore,

(ii) the ribs in their first positions being within an imaginary downward extension of the enlarged diameter portion of the bore so that the mixing head is retractible into said portion of the bore,

(d) a rigid stop member extended from the lower end of the shaft for a distance greater than the altitude of the cone,

(e) resilient means interconnected between the body member and the shaft for biasing the shaft upwardly of the body member,

(f) means carried by the body member for maintaining the shaft in a position relative thereto corresponding to the retracted condition of the mixing head in the bore, and

(g) an operating handle secured to the upper end of the shaft.

9. An agitator for mixing liquids comprising:

(a) a member having a lower end and a bore therethrough open to the lower end,

(b) an operating shaft engaged in the bore for reciprocal movement relative to the body member,

(c) a collapsible frusto-conically configured membranous agitator head having an upper end smaller than its opposite lower end, and

(d) means connecting the head solely to the lower end of the operating shaft and movably mounting the head at its small end to the operating shaft,

=(1) for expansion in response to the resistance of liquids to be mixed to the movement of the head therethrough into an open condition when the operating shaft is moved downwardly from the body member to move the head into engagement with fluids to be mixed, the head in the open condition thereof extending outwardly and downwardly of the operating shaft and having a maximum dimension transversely of the operating shaft greater than the diameter of the bore,

(2) for collapsing into a closed condition when the operating shaft is moved upwardly relative to the body member, the head in the closed condition thereof lying along the elongate extent of the operating shaft and having a maximum dimension less than the diameter of the bore so that the head is retractable into the bore.

it An agitator for mixing liquids comprising:

(a) a tubular axially bored body member having a lower end,

(b) an operating shaft engaged in the body member bore for reciprocation relative to the body member,

(c) a flexible mixing head having a membranous portion of substantially frusto-conical configuration and a plurality of rib members which project toward each other from the small end of the membranous portion to ends spaced from the membranous portion,

(d) means pivotally mounting the ends of the rib members to the lower end of the operating shaft so that -(1) the head expands into an open condition in response to the resistance of liquids to be mixed to the movement of the head therethrough when the operating shaft is reciprocated in the body member to move the head away from the lower end of the body member into engagement of fluids to be mixed, the head in the open condition thereof extending downwardly and outwardly of the shaft, and

(2) the head collapses into a closed condition when the operating shaft is reciprocated to move the head toward the lower end of the body member, the head in its closed condition lying along an imaginary downward extension of the operating shaft, and

(e) an operating handle secured to the upper end of the operating shaft above the upper end of the body member.

11. An agitator according to claim 10 including means carried by the operating shaft and cooperating with the head for preventing over-expansion of the head.

12. An agitator according to claim 10 including means carried by the head at a location spaced from the operating shaft for preventing over-expansion of the head.

13. An agitator for mixing liquids comprising:

(a) a tubular axially bored body member having a lower end and an enlarged diameter portion of the bore open to the lower end of the body member,

(b) an operating shaft engaged in the body member bore for reciprocation relative to the body member,

(c) a flexible mixing head having a membranous portion of substantially frusto-conical configuration and a plurality of rib members which project toward each other from the small end of the membranous portion to ends spaced from the membranous portion, and

(d) means pivotally mounting the ends of the rib members to the lower end of the operating shaft so that (1) the head expands into an open condition in response to the resistance of liquid to be mixed to the movement of the head therethrough when the operating shaft is reciprocated in the body member to move the head away from the lower end of the body member into engagement of fluids to be mixed, the head in the open condition thereof extending downwardly and outwardly of the shaft and having a maximum dimension transversely of the operating shaft greater than the diameter of the enlarged diameter portion of the bore, and

(2) the head collapses into a closed condition when the operating shaft is reciprocated to move the head toward the lower end of the body member, the head in its closed condition lying along an imaginary downward extension of the operating shaft so that the head is retractible into the enlarged diameter portion of the bore.

References Cited by the Examiner UNITED STATES PATENTS 363,674 5/87 Pinel 15-244 609,270 8/98 Flaherty 259135 1,338,277 4/20 Beatty 68215 1,438,794 12/22 Tudor 15-244 X 2,092,353 9/37 Kyseth et al. 259--l44 WALTER A. SCHEEL, Primary Examiner.

WILLIAM I. PRICE, Examiner. 

9. AN AGITATOR FOR MIXING LIQUIDS COMPRISING: (A) A MEMBER HAVING A LOWER END AND A BORE THERETHROUGH OPEN TO THE LOWER END, (B) AN OPERATING SHAFT ENGAGED IN THE BORE FOR RECIPROCAL MOVEMENT RELATIVE TO THE BODY MEMBER, (C) A COLLAPSIBLE FRUSTO-CONICAL CONFIGURED MEMBRANOUS AGITATOR HEAD HAVING AN UPPER END SMALLER THAN ITS OPPOSITE LOWER END, AND (D) MEANS CONNECTING THE HEAD SOLELY TO THE LOWER END OF THE OPERATING SHAFT AND MOVABLY MOUNTING THE HEAD AT ITS SMALL END TO THE OPERATING SHAFT, (1) FOR EXPANSION IN RESPONSE TO THE RESISTANCE OF LIQUIDS TO BE MIXED TO THE MOVEMENT OF THE HEAD THERETHROUGH INTO AN OPEN CONDITION WHEN THE OPERATING SHAFT IS MOVED DOWNWARDLY FROM THE BODY MEMBER TO MOVE THE HEAD INTO ENGAGEMENT WITH FLUIDS TO BE MIXED, THE HEAD IN THE OPEN CONDITION THEREOF EXTENDING OUTWARDLY AND DOWNWARDLY OF THE OPERATING SHAFT AND HAVING A MAXIMUM DIMENSION TRANSVERSELY OF THE OPERATING SHAFT GREATER THAN THE DIAMETER OF THE BORE, (2) FOR COLLAPSING INTO A CLOSED CONDITION WHEN THE OPERATING SHAFT IS MOVED UPWARDLY RELATIVE TO THE BODY MEMBER, THE HEAD IN THE CLOSED CONDITION THEREOF LYING ALONG THE ELONGATE EXTENT OF THE OPERATING SHAFT AND HAVING A MAXIMUM DIMENSION LESS THAN THE DIAMETER OF THE BORE TO THAT THE HEAD IS RETRACTABLE INTO THE BORE. 